The first time I heard the word cyclone was in April 1991. My father had just left his job with the United Nations and moved our family back to Bangladesh. We had lived abroad for 14 years, most of my life, and I suddenly found myself returning to a home I hardly knew. It was a long-held dream of my father's to work for a politically neutral daily newspaper in Bangladesh. He had fought in the war of independence, and during our decade and a half in exile he spoke of little else but giving something back to the country. Eventually he realised he would have to start his own newspaper if it was to be truly impartial, and by the summer of 1991 he had convinced a small group of businessmen to support his venture.

And then, by a stroke of fate, Hossain Mohammad Ershad, the military dictator who had ruled Bangladesh for nine years, was overthrown by a grassroots political movement. The newspaper, called the Daily Star, would start its life in a climate of hope and possibility.

Things did not go so well for me in Bangladesh. When asked to introduce myself on the first day of school, I announced how thrilled I was that democracy had finally been restored to Bangladesh after the cruel and pointless reign of the dictator. Freedom had found us at last, I said, parroting what I had heard at home. I didn't know, as I made that speech, that several of my classmates had parents who were in jail for being closely associated with the just-fallen regime. Needless to say, the welcome was less than warm.

There were other discomforts. There was something wrong with the water supply to our flat, and we had to fill vats of water before the pipes shut down at noon. We had an old car, a cast-off from one of my father's newspaper financiers. Being picked up in it was a daily humiliation. Soon, my father said, we'll buy a new car; we'll move somewhere better.

A few months later, cyclone Gorki crashed into the Bay of Bengal. The young reporters at the Daily Star spent weeks on the Chittagong coast, watching the bodies wash up on the shore. The final tally of casualties topped 130,000. Our new car never materialised, its absence marking an era of austerity for us as the newspaper struggled to establish itself.

Gorki was not the deadliest tropical storm to hit the Bangladesh coast - that honour goes to the Bhola cyclone, which struck on November 12, 1970, and claimed almost half a million lives. Bangladesh was known as East Pakistan at the time, and that cyclone was to have political and historic implications. The West Pakistan administration's handling of the disaster ended the illusion that the two wings of Pakistan were equal, and in the general election a month later, the people of East Pakistan overwhelmingly voted for the pro-independence Awami League, setting in motion a chain of events that would lead to the secession of East Pakistan and the creation of Bangladesh.

Cyclone Sidr comes 37 years after Bhola, and 15 years after Gorki. Much has changed in Bangladesh in that time: the warning systems are far more sophisticated, and many millions of people were taken to safety before the worst of the storm could hit. Nonetheless, as winter sets in, there are still a million homeless, and their livelihood - their crops - has been destroyed.

We don't know whether and to what extent global warming is responsible for the severe weather conditions in Bangladesh. There have been deadly storms in the past; no doubt they will occur again. Nonetheless, there is a strong sense that Bangladesh, so vulnerable to sea-level rises, is on the front line of climate change. Whatever may happen to the planet is already happening here.

Our fears of a world submerged - ravaged by nature, catastrophes apocalyptic in scale - are all writ large on this small patch of earth. Entire villages razed to the ground, trees uprooted and flattened, upside-down ships clogging the rivers and knocking against thousands of drowned cattle, shrimp farms washed away, bodies lost at sea: this is a calamity, in a country that has seen more than its share of disasters.

It is easy to develop disaster fatigue when it comes to Bangladesh. I recently met an American journalist who had been reading about the effect of rising sea levels on our low-lying delta. "Where are all those people going to go?" he asked. "That's a lot of refugees."

I wondered if I should be ashamed at coming from such a blighted place, or angry that he should blame us for a chain of events which may have been set in motion by people in other places. The truth is, many of us have already moved away for reasons that have to do with economics and educational opportunities. And now this diasporic community is spearheading a transformation in the way we respond to disasters. Within hours of the news of cyclone Sidr hitting blogs, broadsheets and Blackberries the world over, expatriate Bangladeshis began appealing for aid. Bloggers in Bangladesh sent updates and photographs of the devastation; Paypal accounts were quickly set up, and a debate began about the best way to send money.

A couple of days ago, someone sent a proposal to a mailing list entitled "Sidr cyclone compensation fund". "What do people think of the following idea? Set up a fund, funded totally by expatriates, to pay cash compensation to families of the deceased? If we set a scale - 5,000 taka (£35) for each adult and 2,500 taka (£17.50) for each child." The fundraising target was set at $275,000 (£133,000), to be raised through global appeals.

Other people replied almost immediately. Some were uncomfortable with placing a price on the victims. "Your suggestion is crude," wrote one. "How do we know whether the victims' families are the ones most in need?" Another person responded: "Can we give the money to the women of the household? Less chances of the money being spent on hooch and gambling."

The fund was set up by the following morning. A name was found (United Bangladesh Appeal); $100,000 has already been pledged.

Our ideas of giving are influenced by the new societies of which we in the diaspora have become part. In Bangladesh, a culture that has favoured giving within family networks, the concept of indirect, relatively anonymous charity is new. It has been introduced by the immigrants who live in societies with fundraisers, leaflets in magazines, TV appeals. These learned forms of giving are making their way into Bangladesh and, with more traditional forms of charity, they are making a difference.

At the heart of this campaigning is a strong sense of responsibility for our fragile homeland. Soon after winning the Nobel Peace prize last year, Mohammad Yunus published an article called A Vision for Bangladesh, in which he pointed out a startling fact: expatriate Bangladeshis send more money home per capita than their Chinese and Indian counterparts. Last year, over $5bn went directly into the Bangladeshi economy, sent from Britain, the US, and, most substantially, from the Middle East.

The story of this money, how it is earned, how it is sent to Bangladesh and why, is one that deserves more space than I have here, but no doubt there is a vein of hope and longing running through every dollar earned abroad, saved and sent home.

I have heard countless times over the past week that we should be grateful the death toll was not higher. That the authorities should be praised for their efficiency in warning people and getting them to safety. That it was worse the last time, much worse. But that does not change the fact that over 3,000 people died on November 15; that many more may yet fall victim to this storm, as their water gets contaminated, and because their crops will yield no harvest, because their jobs and homes and cows have gone. Of course it matters that the situation was not worse. But it is bad enough.

Sixteen years ago my father moved us to Bangladesh believing his country desperately needed him. We were also an example of the fact that immigration occurs in both directions. If extreme weather continues to ravage our country, where will we all go? Far afield, no doubt. But we return home, in person, in the money we send, the tears we shed, the longing in our hearts for a land that is vulnerable - both to the vagaries of fate, and to the destruction that we, collectively, are wreaking upon the world.

· Tahmima Anam's A Golden Age, shortlisted for the Costa first novel award, is published by John Murray

Under the weather

November 1970 A cyclone with 222km winds causes a 20ft tidal surge and kills 500,000 people.

July 1974 Severe flood devastates the grain crop, leading to an estimated 28,000 deaths.

1988 Floods cover three-quarters of the country, killing more than 5,000 and leaving millions homeless.

April 1991 A cyclonic 15ft tidal wave kills up to 138,000.

1998 Flooding from July 12 to September 14 covers 67% of the country, killing 1,200 and causing damage worth $14.5bn.

November 15 2007 Cyclone Sidr hits Bangladesh, killing at least 3,200 and leaving more than two million struggling for necessities such as food, water, shelter and medicines.